Phoebe (moon)
William Henry Pickering stood before a photographic plate on the 18th of March 1899. He held the first image of Phoebe in his hands. The glass plate had been exposed by DeLisle Stewart starting on the 16th of August 1898 at Boyden Observatory near Arequipa, Peru. This was not a visual sighting through an eyepiece. It was the first natural satellite ever discovered using photography. The dark sky over the Andes mountains hid this distant moon for centuries until the chemical process revealed it.
Phoebe orbits Saturn in reverse direction to the planet's rotation. This retrograde path sets it apart from all major moons except Triton. It belongs to the Norse group of irregular satellites that follow highly eccentric trajectories. The moon sits almost four times farther from Saturn than its nearest neighbor Iapetus. Its gravitational influence stretches outward to affect other bodies like S/2006 S 20 and S/2007 S 2. These smaller fragments likely broke off during ancient collision events involving Phoebe itself.
Micrometeoroid impacts eject material from Phoebe's surface into space. This debris forms a massive ring system tilted 27 degrees from Saturn's equatorial plane. The ring extends from 128 to 207 times the radius of Saturn while Phoebe orbits at 215 radii. Infrared telescopes detected this structure because visible light cannot reveal it. Particles within the ring migrate inward and strike Iapetus leading hemisphere. This process contributes to the two-tone coloration observed on that neighboring moon.
Scientists estimate Phoebe contains about 50 percent rock by mass. Spectroscopic observations confirm water ice and carbon dioxide exist on its surface. Radioactive decay melted the interior early in history allowing liquid water to persist for tens of millions of years. This differentiated state solidified before repeated impacts battered the shape into current form. Evidence suggests it originated as a captured centaur from the Kuiper belt rather than forming alongside Saturn.
The Cassini spacecraft flew past Phoebe on the 11th of June 2004 at a distance of roughly 1,900 kilometers. High-resolution images revealed a scarred surface with craters up to 100 kilometers across. Voyager 2 had only seen bright spots on an otherwise dark sphere from 2.2 million kilometers away. The flyby allowed determination of Phoebe's mass with uncertainty of one part in five hundred. Mapping nearly the entire surface took advantage of its short rotation period of nine hours and 17 minutes.
The International Astronomical Union officially named 24 craters in 2006 following specific conventions. All features except Leto Regio bear names from characters in the Jason and Argonauts legend. Crater Jason measures 101 kilometers while Iphitus spans 22 kilometers. These designations honor figures like Calais son of Boreas or Peleus father of Achilles. The naming process reflects Greek mythology traditions applied to outer solar system bodies since 2005.
Up Next
Continue Browsing
Common questions
When was the moon Phoebe discovered?
William Henry Pickering held the first image of Phoebe on the 18th of March 1899. The glass plate had been exposed by DeLisle Stewart starting on the 16th of August 1898 at Boyden Observatory near Arequipa, Peru.
How does the orbit of Phoebe differ from other moons around Saturn?
Phoebe orbits Saturn in reverse direction to the planet's rotation. This retrograde path sets it apart from all major moons except Triton and places it within the Norse group of irregular satellites that follow highly eccentric trajectories.
What is the origin of the Phoebe ring system around Saturn?
Micrometeoroid impacts eject material from Phoebe's surface into space to form a massive ring system tilted 27 degrees from Saturn's equatorial plane. The ring extends from 128 to 207 times the radius of Saturn while Phoebe orbits at 215 radii.
Did the Cassini spacecraft fly past the moon Phoebe?
The Cassini spacecraft flew past Phoebe on the 11th of June 2004 at a distance of roughly 1,900 kilometers. High-resolution images revealed a scarred surface with craters up to 100 kilometers across during this encounter.
When did the International Astronomical Union name craters on Phoebe?
The International Astronomical Union officially named 24 craters in 2006 following specific conventions. All features except Leto Regio bear names from characters in the Jason and Argonauts legend.